#include <stdio.h>
#include <stdlib.h>

int seq(int n){
	if(n == 1||n == 2) n = 1;
	return seq(n-1) +seq(n-2);
}
int main(){
	int res,i;
	printf("请输入项数！\n");
	scanf("%d",i);
	res = seq(i);
	if(res == -1){
		printf("项数非法！\n");
		exit(0);
	}
	printf("%d\n",res);
}
